The present invention, in some embodiments thereof, relates to an orthodontic bracket and, more particularly, but not exclusively, to a bracket with no moving parts.
Orthodontic tooth movement is commonly generated by prolonged pressure applied to a tooth. It is generally believed that the tooth movement results from a cascade of events initiated by mechanical forces which alter the stress-strain distribution within the periodontal ligament (PDL) and results in remodeling of the surrounding alveolar bone, bone resorption occurs in areas of pressure and bone formation occurs in areas of tension.
An excessive orthodontic force produces hyalinization of the PDL and undermines bone resorption, impeding efficient bone remodeling. This phenomenon suggests that there is a maximum stress above which the bone remodeling rate decreases. The application of light and continuous forces results in reduced hyalinization, direct bone resorption, and relatively rapid tooth movement. It has been hypothesized that the key factor is not the absolute magnitude of the delivered force that is important, but rather, the distributed load or stress in the surrounding periodontal ligament and resultant strain.
In general, the following directions of force (as applied to teeth) are recognized:
Buccal—force applied away from the inside the mouth.
Palatal—force applied towards the inside of the mouth.
Mesial—force, in a direction along the dental arch, towards the front of the mouth.
Distal—force, in a direction along the dental arch, towards the back of the mouth.
Apical—force applied towards the apex of the roots of a tooth.
Incisor—force applied towards the edge of the crown of a tooth.
Tipping—force which moves the crown more than the root
Torque—force which moves the root more than the crown
Upright force which makes a tooth more perpendicular to gum
Translation—force which moves a tooth along the gum.
Rotation—tooth is rotated around an axis connecting its root and its crown.
In typical orthodontic situations, multiple teeth need to be moved and have their orientation changed. A standard way of achieving such multiple movements, is to attach a bracket to each of a plurality of teeth (at a buccal side or a palatal side) and interconnect the brackets using a wire. The wire and optional springs/elastic bands, apply the tooth correction forces. Additional plates, or other tools may be necessary to achieve the desired balance of forces on the teeth, a snot all forces can currently be applied using brackets.
In a typical methodology, the brackets are carefully attached so that they would be aligned if the teeth were aligned and a wire connected to the brackets in a manner where it can slide (no friction). This step of positioning the brackets is considered very important as it is generally undesirable to reconnect brackets due to misplacement and also undesirable to not align the teeth due to bracket misplacement. This wire applies forces as it tries to straighten, for example, due to its bending by relative positions of brackets on neighboring teeth. Translation forces may be applied using springs between teeth (brackets). After some time, the teeth move and the wire cannot apply significant force. At this time, the old wire is removed and a wire which is thicker is used, and which is better coupled to the bracket, for example, it may be rigidly held by friction in the bracket. This allows the wire to apply greater forces than the first wire and thus achieve the final small corrections to completely align the teeth. It is currently accepted that with friction based movement, lower rates of teeth alignment are achieved.
While the wire may be attached to the bracket using various tying mechanisms, it has become common to use self-ligating brackets. Active self ligating brackets are those with a spring clip that can press against the archwire. Passive self-ligating brackets are brackets in which the clip, ideally, does not press against the wire and is comparable to a buccal tube.
As a generalization, self-ligating brackets show excellent performance in vitro with smaller wires that are used early in treatment. However, when larger wires were used such as 0.016×0.022 in and 0.019×0.025 in nickel-titanium in the austenitic phase, no differences were found between self-ligating brackets and conventional brackets. Self-ligating brackets demonstrated low frictional resistance only up to certain size archwires in a 0.022-in slot.
Several investigators and many clinicians reported difficulties in finishing cases with self-ligating brackets. Particularly, torque, tip and rotation control can be compromised due to the greater play of the archwire in the slot of self-ligating brackets.
It should be noted that some visits during a treatment relate to failure of the moving parts of the self-ligating brackets, however, this is commonly considered a worthwhile tradeoff.
Many brackets have been developed with various design tradeoffs.
In the following US patents, self-ligating orthodontic brackets were described: U.S. Pat. No. 7,306,457 to Vigolo; U.S. Pat. No. 6,682,345 to Kesling et. al; U.S. Pat. No. 6,733,286 to Abels et. al; U.S. Pat. No. 6,358,045 to Farzin-Nia et. al; U.S. Pat. No. 6,302,688 to Jordan et. al; U.S. Pat. No. 6,071,119 June 2000 Christoff et. al and U.S. Pat. No. 5,711,666 to Hanson. US publication 20020197581 to Georgakis, Evangelos G.; et. al; also described a self-ligating bracket.
The following articles describe various properties of existing and hypothesized future brackets:    1. Von Bohl M M J, Von Den Hoff J W, A M. K-J. Focal hyalinization during experimental tooth movement in beagle dogs. Am J Orthod Dentofac Orthop 2004; 125:615-623.    2. Von Bohl M M J, Von Den Hoff J W, A M. K-J. Changes in the periodontal ligament after experimental tooth movement using high and low continuous forces in beagle dogs. Angle Orthod 2004; 74:16-25.    3. Melsen B. Biological reaction of alveolar bone to orthodontic tooth movement. Angle Orthod 1999; 69:151-158.    4. Reitan K. Biomechanical principles and reactions. In: Graber T M S B, editor. Orthodontics, Current Orthodontic Concepts and Techniques. St Louis: The C.V. Mosby Co.; 1985. p. 101-192.    5. Burstone C. The biphysics of bone remodeling during orthodontics-optimal force considerations. In: Norton L A, C J. B, editors. The Biology of Tooth Movement. Boca Raton: CRC Press; 1986. p. 321-333.    6. Tanne K, Sakuda M, Burstone C. Three dimensional finite element analysis for stress in the periodontal tissue by orthodontic forces. Am J Orthod Dentofac Orthop 1987; 92:499-505.    7. Kesling P C. Dynamics of the tip-edge bracket. Am J. Orthod. 1989; 96:16-28.    8. Damon D H. The Damon low-friction bracket: a biologically compatible straight-wire system. J Clin Orthod. 1998; 32:670-680.    9. Kojima Y, Fukui H., Miyajimac K., The effects of friction and flexural rigidity of the archwire on canine movement in sliding mechanics: A numerical simulation with a 3-dimensional finite element method. Am J Orthod Dentofac Orthop 2006:130, 3; 275.-275    10. Kojima Y, Fukui H. Numerical simulation of canine retraction by sliding mechanics. Am J Orthod Dentofacial Orthop. 2005; 127:542-551    11. Henao S P, Kusy R P. Evaluation of the frictional resistance of conventional and self-ligating bracket designs using standardized archwires and dental typodonts. Angle Orthod. 2004; 74:202-211    12. Rinchuse D. Ja, Miles B P G., Self-ligating brackets: Present and future Am J Orthod Dentofacial Orthop 2007; 132:216-22    13. Miles P G. SmartClip versus conventional twin brackets for initial alignment: Is there a difference?. Aust Orthod J. 2005; 21:123-127    14. Harradine N W T. Self-ligating brackets and treatment efficiency. Clin Orthod Res. 2001; 4:220-227.    15. Eberting J J, Straja S R, Tuncay O C. Treatment time, outcome, and patient satisfaction comparisons of Damon and conventional brackets. Clin Orthod Res. 2001; 4:228-234.    16. Harradine N W T, Birnie D J. The clinical use of Activa brackets. Am J Orthod Dentofacial Orthop. 1996; 109:319-328
The disclosures of all of the above articles, patents and publications are incorporated herein by reference.